The key etiologic factor responsible for accelerated vascular disease in diabetes mellitus remains unknown. Endothelial cell damage, as a conquence of sustained hyperglycemia, may be an initiating factor that is necessary but not sufficient for the development of the complication. The endothelium is a likely target tissue because it often manifests non-insulin dependent facilitated glucose transport and is enriched in aldose reductase activity, two phenomena which are characteristic of target tissues. Abnormal polyol, myoinositol metabolism and impaired Na+, K+-ATPase activity have been linked in the experimental diabetic peripheral nerve, lens and renal glomeruli where the metabolism of glucose is similar. It has recently been recognized that phosphoinositide metabolism may help to regulate Na+-pump function. Increased polyol pathway activity, abnormal myo- inositol metabolism and complications analogous to those seen in the diabetic state such as cataracts and peripheral nerve dysfunction are also part of galactose toxicity supporting the hypothesis that a high sugar milieu per se is sufficient to initiate diabetic tissue damage. The purpose of this study is to utilize aortic endothelial cells in culture as a model for the study of diabetic angiopathy. Endothelial cells cultured in a medium containing high concentrations of glucose or galactose will demonstrate increased polyol pathway activity and depletion of myo-inositol both of which may be corrected by concomitantly incubating with an aldose reductase inhibitor. While decreased myo-inositol levels in these cells does not lead to decreased levels of phosphatidylinositol, there is a significant impairment in phosphatidylinositol turnover which can not be corrected by simultaneous inhibition of aldose reductase. This is important because the major tenet of the prevailing hypothesis concerning abnormal myo-inositol metabolism in diabetes is that myo-inositol depletion is deleterious only because it will result in a secondary depletion of cell phosphatidylinositol leading to defective regulation of Na+, K+-ATPase activity. Our studies suggest that an abnormality in phosphoinositide metabolism is another independent effect of elevated glucose or galactose levels. In this study we will determine the mechanism whereby high sugar levels produce a depletion of myo-inositol, the biochemical lesion responsible for impaired phosphoinositide turnover and how both relate to impaired electrolyte and water homeostasis. Reversal of the various biochemical and physiological abnormalities including potential defective cell proliferation will be accomplished by using aldose reductase inhibitors or supplementation with myo-inositol and/or arachidonate.